曹耘豪的博客

Alibaba的TransmittableThreadLocal

  1. TransmittableThreadLocal特性
  2. 先看看InheritableThreadLocal的实现
  3. 案例对比
    2. new Thread() + InheritableThreadLocal，可取到
    3. 线程池 + InheritableThreadLocal，不可取到
    4. new Thread() + TransmittableThreadLocal，和InheritableThreadLocal一致
    5. 原生线程池 + TransmittableThreadLocal，不可取到
    6. TTL包装器线程池 + TransmittableThreadLocal，可取到
  4. 大致原理
    1. 核心方法解释
  5. 其他特性

TransmittableThreadLocal特性

先看看InheritableThreadLocal的实现

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if (inheritThreadLocals && parent.inheritableThreadLocals != null)
    this.inheritableThreadLocals =
        ThreadLocal.createInheritedMap(parent.inheritableThreadLocals);

案例对比

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inheritThreadLocals

new Thread() + InheritableThreadLocal，可取到

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InheritableThreadLocal<String> threadLocal = new InheritableThreadLocal<>();
threadLocal.set("a");

new Thread(() -> {System.out.println(threadLocal.get());}).start();
// 输出a

线程池 + InheritableThreadLocal，不可取到

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ExecutorService executor = Executors.newFixedThreadPool(1);
// 先初始化进程，确保线程初始化时上下文中没有ThreadLocal信息
executor.submit(() -> {System.out.println("init");}).get();

InheritableThreadLocal<String> threadLocal = new InheritableThreadLocal<>();
threadLocal.set("a");

executor.execute(() -> {System.out.println(threadLocal.get());});
// 输出null

new Thread() + TransmittableThreadLocal，和InheritableThreadLocal一致

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TransmittableThreadLocal<String> threadLocal = new TransmittableThreadLocal<>();
threadLocal.set("a");

new Thread(() -> {System.out.println(threadLocal.get());}).start();
// 输出a

原生线程池 + TransmittableThreadLocal，不可取到

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ExecutorService executor = Executors.newFixedThreadPool(1);
// 先初始化进程，确保线程初始化时上下文中没有ThreadLocal信息
executor.submit(() -> {System.out.println("init");}).get(); 

TransmittableThreadLocal<String> threadLocal = new TransmittableThreadLocal<>();
threadLocal.set("a");

executor.execute(() -> {System.out.println(threadLocal.get());});

// 输出
// init
// null

TTL包装器线程池 + TransmittableThreadLocal，可取到

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ExecutorService executor = TtlExecutors.getTtlExecutorService(Executors.newFixedThreadPool(1));
// 先初始化进程，确保线程初始化时上下文中没有ThreadLocal信息
executor.submit(() -> {System.out.println("init");}).get(); 

TransmittableThreadLocal<String> threadLocal = new TransmittableThreadLocal<>();
threadLocal.set("a");

executor.execute(() -> {System.out.println(threadLocal.get());});

// 输出
// init
// a

大致原理

核心方法解释

其他特性

  技术 / Java